Smoke filters



Feb. 27, 1968 H. J. DAVIS ETAL 3,370,595

SMOKE FILTERS Filed Jan. 4. 1965 be; uu Q kkb Q a w m 0 b v n N o United States latent C 3,37tl,595 SMGKE FILTERS Howard J. Davis, Murray Hill, Robert F. Busse, New

Providence, and Thomas W. George, Berkeley Heights,

N.J., assignors to Celanese Corporation, a corporation of Delaware Filed Jan. 4, 1965, Ser. No. 423,105 13 Claims. (Cl. 131-266) ABSTRACT OF Tim DISCLOSURE Smoke filters of multi-segrnent construction containing at least one segment carrying a selective removal agent such as activated carbon and a low amount of plasticizer, and at least one second segment being generally free of said removal agent and containing a high percentage of plasticizer, the filters being characterized by enhanced smoke removal efficiencies over longer storage times as compared to conventional removal agent containing smoke filters.

This invention relates to smoke filters. More specifically, this invention relates to cigarette smoke filters or filter tips.

The smoke stream of a cigarette is a mixture; it consists of a particulate phase and a gas or vapor phase. Both phases, but especially the particulate phase, contain filterable substances commonly known as tars. Phenol and cresols are found in the weak acid fraction of smoke condensate. The gas, or, more accurately, vapor phase, includes light hydrocarbons, isoprene, furan, acetaldehyde, Z-methyl furan, propionaldehyde, isobutyraldehyde, acrolein, methanol, acetone, methyl ethyl ketone, and toluene. It is now known that physiologically some of these compounds are harmful and are variously carcinogens, co-carcinogens or promoters, and vapor phase irritants. Smoke removal efficiency is the percentage of the total tars or condensate in the over-all cigarette smoke stream'which is removed by a given filter tip; accordingly, the total level of tars can be controlled by means of greater smoke removal efiiciency. However, this is not a means of selectively removing deleterious substances from the smoke stream and, furthermore, is limited by the fact that smoke removal efiiciency is increased by increasing the pressure drop across the filter and a filter with too high pressure drop results in a cigarette which is difiicult or uncomfortable to draw upon.

Attempts have been made to selectively remove from the smoke stream especially deleterious substances by incorporating activated carbon in the cigarette filter. However, it has been found that the efiectiveness of filter tips containing activated carbon very rapidly decreases after about three weeks from the time the cigarette is made. This is very important when one considers that generally cigarettes are at least three weeks old by the time they reach the consumer and are smoke-d. It is hypothesized that the reason for this great decrease in the effectiveness of the cigarette filter is that various organic and inorganic additives such as humectants, flavoring agents and top dressing are added to smoking tobacco, which additives initially are not in equilibrium with the filter tip and, apparently, after a period of about two months an equilibrium is established which equilibrium occupies many of the sorptive sides of the filter medium.

Another problem especially significant with cigarette filters consisting of filaments interspersed with which is activated carbon, is de-activation of the carbon by the plasticizer carried by the filter. Generally, when filte tips are made of filamentary material whether or not there is interspersed activated carbon, a plasticizer for the filamentary material is used in order to impart to the filter tip adequate firmness. Generally, the amount of plasticizer carried by the filamentary material is more than 5% and less than 10% by weight, based on the weight of the filamentary material. Apparently, some of the plasticizer migrates from the filaments to the activated carbon and thereby substantially deactivates the carbon.

According to the present invention, it has now been found possible to provide filters in which the foregoing problems are eliminated or substantially mitigated.

In accordance with the present invention, there is provided a smoke filter comprising a plurality of sections in series, at least one of said sections being a high plasticizer section (i.e., containing a relatively high proportion of plasticizer) comprising filamentary material and carrying at least about 10% by Weight of plasticizer for such filamentary material (which is a relatively high proportion), based on the weight of said filamentary material, and at least one other of said sections being a low plasticizer section (i.e., a section containing a relatively low proportion of plasticizer) comprising filamentary material interspersed with particles of a selective removal agent and carrying a maximum of about 5% plasticizer for said filamentary material (which is a relatively low proportion of plasticizer), based on the weight of said filamentary material.

Any filamentary material may be used. Also, functional equivalents of filamentary materials such as polymeric flakes or strips of paper may be used. Because of its good filtration properties and ease of processability into cigarette filters, it is preferred that the filamentary material comprise cellulose acetate. The term cellulose acetate as used in the present specification and claims, includes both secondary cellulose acetate, i.e., cellulose acetate having an acetyl value of about 5058% but preferably the well known secondary cellulose acetate of commerce having an acetyl value of about 5355% and cellulose triacetate, i.e., cellulose acetate having an acetyl value of at least 59%; acetyl value is calculated as combined acetic acid by weight and has a theoretical maximum of 62.5%. Secondary cellulose acetate is especially preferrred because it is somewhat more conveniently plasticizable than cellulose triacetate.

Any selective removal agent may be used. Polyethylene glycols and activated carbon are examples of selective removal agents. Activated carbon appears to be especially effective and a particularly useful form thereof is activated charcoal.

It is highly preferred that the high plasticizer section carry more than 12% plasticizer on the above-explained basis, which basis for the sake of convenience will hereafter beimplied and not explicitly stated. It is also highly preferred that the low plasticizer section carry less than 4% plasticizer. The maximum plasticizer content in the high plasticizer section may be up to about 50%. It is preferred that the low plasticizer section carry a minimum of about 1% of plasticizer. Selection of a plasticizer is not critical; however, triacetin and triethyl citrate are preferred plasticizers since to some extent they selectively sorb acidic compounds such as phenol and cresols from the smoke stream and thereby add to the effectiveness of the filter.

Also, in accordance with the present invention, there is provided a smoke filter simply comprising filamentary material interspersed with particles of a selective removal agent and carrying less than 4% plasticizer and preferably a minimum of about 1% of plasticizer. Cellulose acetate and, especially secondary cellulose acetate are the preferred filamentary materials and triacetin and triethyl citrate are the preferred plasticizers. Functional equivalents material is intended to include such functional equivalents as above mentioned.

Unlike the cigarette filters of the prior art, the filters V of the present invention, when incorporated in a cigarette,

do not significantly decrease in effectiveness until a period of about two full months has passed; most cigarettes reach the consumer and are smoked within this period of time. It is hypothesized that the plasticizer in the filters of the present invention acts as a scavenger for the organic and inorganic tobacco additives referred to above which normally enter into an equilibrium state with the filter; apparently, in the filters of the present invention, the equilibrium is established primarily with the plasticizer and thus the sorptive sites of both the filamentary material and the selective removal agent are left free, and not until a period of about two full months has passed do these parts of the filter begin to substantially enter into the equilibrium. At the same time, Where a selective removal agent such as activated carbon is interspersed with the filamentary material, the plasticizer content carried by the filamentary material in which the selective removal agent is interspersed is kept sufficiently low so that the selective removal agent is not significantly contaminated and thereby decreased in effectiveness. Also, in any portion of the filter which is not interspersed with selective removal agent, a high plasticizer content it provided because thereby the selective removal properties of the plasticizer can be taken advantage of without the disadvantage of contamination of selective removal agent. In this respect, it should be noted that, in the language of the present specification and claims, selective removal agent or smoke filter agent are intended to denote materials other than plasticizer and are intended not to denote plasticizer though, as pointed out above, the plasticizer itself may have a significant selective removal effect.

The efiectiveness of the smoke filters of the present invention can especially significantly be represented in terms of recently noted physiological eifects of cigarette smoke. The human respiratory system is provided with cilia which, apparently, filter whatever one inhales. These cilia .wave back and forth with a steady frequency under normal conditions. It is observed that cigarette smoke tends to interfere with the normal operation of the cilia. The steady rhythmic action of the cilia is disrupted by cigarette smoke and the overall effect is to greatly decrease the frequency at which the cilia wave back and forth; this efiect is known as ciliastasis.

The inner demibranch of a clam gill is also provided with cilia. These cilia apparently function very much in the same way as human respiratory cilia, however filtering water rather than air. In order to perform a bioassay of cigarette smoke, the cigarette smoke is passed over a tissue section of clam gill containing these cilia; to simulate cigarette smoking, the smoke is passed over the tissue section in puff-like quantities at pufi-like intervals. The frequency of the cilia motion is measured by use of an electronic stroboscope. In this manner the ciliastatic eifect of various cigarettes, with and without filters, may be measured. The frequency of cilia motion is plotted against the number of pufis.

EXAMPLE To a tow of 50,000 secondary cellulose acetate filaments of I-beam cross section and 2.5 denier per'filament there is applied by spraying 14% of triacetin and the tow is made into ten millimeter length tips; conventional cigarette filter manufacturing apparatus is used. Similarly, ten millimetertips are prepared from a tow of 45,000 secondary cellulose acetate filaments of regular cross-section and 5.0 denier per filament with a plasticizer application of 3.8% of triacetin and, also, an application of 62 milligrams of 50X 200 mesh activated charcoal per ten mil- 4 limeter tip. The total Weight of the first mentioned tip is milligrams and the total weight of the latter tip is 132 milligrams. The non-charcoal tip is attached to a non-filter cigarette and the non-charcoal and charcoal tips are attached together as a dual tip to a second non-filter cigarette with the non-charcoal section at the end to avoid the passage of charcoal to the smokers mouth. Both of these filter cigarettes are checked for ciliastatic effect and compared in this'regard to conventional filter and non-filter cigarettes. The graph shows a plot of cilia frequency against the number of puffs. Curve one is for a cigarette with the above described dual filter tip according to the present invention; curve two is for a cigarette with the above described single component activated charcoal-containing filter tip according to the present invention; curve three is for a widely sold representative activated charcoal-containing filter tip cigarette; curve four is for a widely sold representative non-charcoal secondary cellulose acetate,

filter tip cigarette and curve five is for a widely sold representative non-filter cigarette. It is apparent from the graph that cigarettes tipped with the filters of the present invenion cause a much lesser ciliastatic effect than the cigarettes of various types of the prior art. This improvement is due to the fact that the filters of the present invention are substantially more effective at selectively removing the aforementioned deleterious compounds from a cigarette smoke stream; this is demonstrable, for example, by

chromatographic analysis of the smoke stream drawn from the cigarettes.

According to the present invention, when activated carbon is incorporated in a filter tip or filter tip section it is preferred to use at least about 40 milligrams and up to about 90 milligrams or more of activated carbon per 10 mm. of tip length. The amount of activated carbon necessary to achieve a given degree of filtration effectiveness is, of course, to some extent dependent-upon the kind of activated carbon used and the mesh of the activated carbon; generally speaking the finer the mesh-the less the quantity of activated carbon necessary to achieve a given degree of filtration eifectiveness. The tows or other filamentary or functionally equivalent materials themselves from which the filter tips are made are conventional; i.e., the present invention does not lie in the filamentary material or functional equivalent thereof per se.

It is to be understood -that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A smoke filter comprising a plurality of sections in series, at least one of said sections being a high plasticizer section comprising filamentary material and carrying at least about 10% by weight of plasticizer for said filamentary material, based on the weight of said filamentary material, and at least one other of said sections being a low plasticizer section comprising filamentary mtaerial interspersed with particles of a smoke filter agent whose smoke filtering ability would be masked by a high amount of plasticizer and carrying a maximum of about 5% of plasticizer for said filamentary material, based on the weight of said filamentary material.

2. The smoke filter defined in claim 1, wherein: the filamentary material of each of said sections is comprised of cellulose acetate.

3. The smoke filter defined in claim 2, wherein: the filamentary material of each of said sections is comprised of secondary cellulose acetate.

4. The smoke filter defined in claim 3, wherein: said agent is activated carbon.

5. The smoke filter defined in claim 4, wherein: said agent is activated charcoal.

6. A cigarette filter comprising a plurality of sections in series,

at least one of said sections comprising a mass of supporting cellulose acetate filamentary material carrying at least 12 percent by weight, based on the weight of the filamentary material, of an organic ester plasticizer therefor,

and at least one other of said sections comprising a mass of supporting cellulose acetate filamentary material carrying less than 4 percent by weight, based on the weight of the filamentary material, of an organic ester plasticizer therefor, and from about 40 to about 90 mg., per 10 millimeters of standard tip length, of a smoke filter agent whose smoke filtering ability would be masked by a high amount of plasticizer said filter being characterized by enhanced retention of smoke removal efiiciency over periods of at least three weeks as compared to conventional cigarette filters, and

a delivered smokestream, upon treatment of the combustion products of a conventional cigarette tobacco column, yielding reduced ciliastasis in ciliary tissue derived from the inner demibranch of a clam gill.

7. The smoke filter defined in claim 6, wherein: said low plasticizer section carries a minimum of about 1% by weight of plasticizer for said filamentary material, based on the weight of said filamentary material.

8. The smoke filter defined in claim 6, wherein: said plasticizer comprises a compound selected from the group consisting of triacetin and triethyl citrate.

9. The smoke filter defined in claim 8, wherein: said plasticizer comprises triacetin.

10. The smoke filter defined in claim 8, wherein: said plasticizer comprises triethyl citrate.

11. A method of selectively filtering smoke comprising treating said smoke, in successive zones arranged in any order, with a filter segment comprising a mass of supporting fibrous material carrying a plasticizer therefor and a smoke filter agent whose smoke filtering ability would be masked by a high amount of plasticizer and another filter segment comprising a mass of supporting fibrous material carrying a plasticizer therefor, said latter segment being generally free of said agent, the amount of plasticizer in said former segment being considerably less than the amount of plasticizer in said latter segment.

12. The cigarette filter of claim 6, wherein said agent is selected from the group consisting of activated carbons and charcoals and polyethylene glycols.

13. The cigarette filter of claim 6, said agent-containing segment being disposed upstream of at least one other filter segment.

References Cited UNITED STATES PATENTS 3,032,829 5/1962 Mahoney et al.

3,101,723 8/1963 Seligman et al. 131-266 3,169,535 2/1965 Lassiter et a1. l31-10.7 3,190,294 6/1965 Dunlap 131-267 SAMUEL KOREN, Primary Examiner. D. I. DONOHUE, Assistant Examiner. 

